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CONTENTS
Volume 74, Number 3, May10 2020
 

Abstract
Non-destructive tests are commonly used in construction industry to access the quality and strength of concrete. However, till date there is no non-destructive testing method that can be adopted to evaluate the bond condition of reinforced concrete beams. In this regard, the presented research work details the use of ultra-sonic pulse velocity test method to evaluate the bond condition of reinforced concrete beam. A detailed experimental research was conducted by testing four identical reinforced concrete beam samples. The samples were loaded in equal increments till failure and ultra-sonic pulse velocity readings were recorded along the length of the beam element. It was observed from experimentation that as the cracks developed in the sample, the ultra-sonic wave velocity reduced for the same path length. This reduction in wave velocity was used to identify the initiation, development and propagation of internal micro-cracks along the length of reinforcement. Using the developed experimental methodology, researchers were able to identify weak spots in bond along the length of the specimen. The proposed method can be adopted by engineers to access the quality of bond for steel reinforcement in beam members. This allows engineers to carryout localized repairs thereby resulting in reduction of time, cost and labor needed for strengthening. Furthermore, the methodology to apply the proposed technique in real-world along with various challenges associated with its application have also been highlighted.

Key Words
ultra-sonic pulse velocity test; bond assessment; incremental loading; micro-crack development; internal crack propagation; real-world application strategy

Address
Department of Mechanical and Energy Engineering, College of Engineering, Imam Abdulrahman Bin Faisal University, P.O. Box 1982, Dammam 31441, Eastern Province, Saudi Arabia

Abstract
This study presents a practical application of topology optimization (TO) technique to seek the best form of perforated steel plate shear walls (PSPSW) in simple frames. For the numerical investigation, a finite element model is proposed based on the recent particular form of PSPSW that is called the ring-shaped steel plate shear wall. The TO is applied based on the sensitivity analysis to maximize the reaction forces as the objective function considering the fracture tendency. For this purpose, TO is conducted under a monotonic and cyclic loading considering the nonlinear behavior (material and geometry) and buckling. Also, the effect of plate thickness is studied on the TO results. The final material volume of the optimized plate is limited to the material volume of the ring-shaped plate. Finally, an optimized plate is introduced and its nonlinear behavior is investigated under a cyclic and monotonic loading. For a more comprehensive view, the results are compared to the ring-shaped and four usual forms of SPSWs. The material volume of the plate for all the models is the same. The results indicate the strength, load-carrying, and energy dissipation in the optimized plate are increased while the fracture tendency is reduced without changing the material volume.

Key Words
topology optimization; perforated steel plate shear walls; simple frame; cyclic loading; sensitivity analysis

Address
Faculty of Civil Engineering, Shahid Rajaee Teacher Training University, Tehran, Iran

Abstract
The present investigation is concerned with two dimensional deformation in a non local thermoelastic solid with two temperatures due to time harmonic sources. The nonlocal thermoelastic solid is homogeneous with the effect of two temperature parameters. Fourier transforms are used to solve the problem. The bounding surface is subjected to concentrated and distributed sources. The analytical expressions of displacement, stress components and conductive temperature are obtained in the transformed domain. Numerical inversion technique has been applied to obtain the results in the physical domain. Numerical simulated results are depicted graphically to show the effect of nonlocal parameter and frequency on the components of displacements, stresses and conductive temperature. Some special cases are also deduced from the present investigation.

Key Words
thermoelasticity; nonlocality; nonlocal theory of thermoelasticity; Eringen model of nonlocal theories; two temperature; time harmonic sources

Address
Parveen Lata; Department of Basic and applied Sciences, Punjabi University Patiala, India
Sukhveer Singh: Punjabi University APS Neighbourhood Campus, Dehla Seehan, India

Abstract
Based on the dynamic tests of recycled aggregate concrete (RAC) short columns confined by the hoop reinforcement, the dynamic failure mechanism and the mechanical parameters related to the constitutive relation of confined recycled aggregate concrete (CRAC) were investigated thoroughly. The fracturing sections were relatively flat and smooth at higher strain rates rather than those at a quasi-static strain rate. With the increasing stirrup volume ratio, the crack mode is transited from splitting crack to slipping crack constrained with large transverse confinement. The compressive peak stress, peak strain, and ultimate strain increase with the increase of stirrup volume ratio, as well as the increasing strain rate. The dynamic confining increase factors of the compressive peak stress, peak strain, and ultimate strain increase by about 33%, 39%, and 103% when the volume ratio of hoop reinforcement is increased from 0 to 2%, but decrease by about 3.7%, 4.2%, and 9.1% when the stirrup spacing is increased from 20mm to 60mm, respectively. This sentence is rephrased as follows: When the stirrup volume ratios are up to 0.675%, and 2%, the contributions of the hoop confinement effect to the dynamic confining increase factors of the compressive peak strain and the compressive peak stress are greater than those of the strain rate effect, respectively. The dynamic confining increase factor (DCIF) models of the compressive peak stress, peak strain, and ultimate strain of CRAC are proposed in the paper. Through the confinement of the hoop reinforcement, the ductility of RAC, which is generally slightly lower than that of NAC, is significantly improved.

Key Words
recycled aggregate concrete (RAC) short column; confined recycled aggregate concrete (CRAC); dynamic confining effect; dynamic confining increase factor (DCIF); compressive peak stress; compressive peak strain; compressive ultimate strain

Address
Changqing Wang:
1Jiangsu Key Laboratory of Environmental Impact and Structural Safety in Engineering, China University of Mining & Technology (CUMT), Xuzhou, Jiangsu 221116, China
2Department of Civil Engineering, Shanghai University, Shanghai 200444, China
3Department of Building Engineering, College of Civil Engineering, Tongji University, Shanghai 200092, China
4Jiangsu Collaborative Innovation Center for Building Energy Saving and Construction Technology, Xuzhou, Jiangsu 221116, China
Jianzhuang Xiao: Department of Building Engineering, College of Civil Engineering, Tongji University, Shanghai 200092, China

Abstract
The focus of this paper is to develop an analytical approach based on an efficient shear deformation theory with stretching effect for bending stress analysis of cross-ply laminated composite plates subjected to transverse parabolic load and line load by using a new kinematic model, in which the axial displacements involve an undetermined integral component in order to reduce the number of unknowns and a sinusoidal function in terms of the thickness coordinate to include the effect of transverse shear deformation. The present theory contains only five unknowns and satisfies the zero shear stress conditions on the top and bottom surfaces of the plate without using any shear correction factors. The governing differential equations and its boundary conditions are derived by employing the static version of principle of virtual work. Closed-form solutions for simply supported cross-ply laminated plates are obtained applying Navier's solution technique, and the numerical case studies are compared with the theoretical results to verify the utility of the proposed model. Lastly, it can be seen that the present outlined theory is more accurate and useful than some higher-order shear deformation theories developed previously to study the static flexure of laminated composite plates.

Key Words
stress analysis; cross-ply laminated plates; parabolic load; line load; static flexure

Address
Soufiane Abbas, Mohamed Benguediab: Laboratory of Materials and Reactive Systems (LMRS), University of Sidi Bel Abbes, Faculty of Technology,
Mechanical Engineering Department, Algeria
Soumia Benguediab, Kada Draiche, Ahmed Bakora: Material and Hydrology Laboratory, University of Sidi Bel Abbes, Faculty of Technology, Civil Engineering Department, Algeria
Soumia Benguediab: Université Dr Tahar Moulay, Faculté de Technologie, Département de Génie Civil et Hydraulique,
BP 138 Cité En-Nasr 20000 Saida, Algeria
Kada Draiche: Department of Civil Engineering, Ibn Khaldoun University, BP 78 Zaaroura, 14000 Tiaret, Algeria

Abstract
The structural performance of cold-formed steel (CFS) built-up battened columns were numerically investigated in this paper. The built-up column sections were formed by connecting two-lipped channels back-to-back, with a regular spacing of battens plates, and have been investigated in the current study. Finite element models were validated with the test results reported by the authors in the companion paper. Using the validated models, the parametric study was extended, covering a wider range of overall slenderness to assess the accuracy of the current design rules in predicting the design strengths of the CFS built-up battened columns. The parameters viz., overall slenderness, different geometries, plate slenderness (b/t ratio) and yield stress were considered for this study. In total, a total of 228 finite element models were analyzed and the results obtained were compared with current design strength predicted by Effective Width Method of AISI Specifications (AISI S100:2016) and European specifications (EN1993-1-3:2006). The parametric study results indicated that the current design rules are limited in predicting the accuracy of the design strengths of CFS built-up battened columns. Therefore, a design equation was proposed for the AISI and EC3 specifications to predict the reliable design strength of the CFS Built-up battened columns and was also verified by the reliability analysis.

Key Words
cold-formed steel; effective width method; lipped channel; numerical study; battened column; reliability analysis; built-up columns

Address
Vijayanand S: Department of Civil Engineering, Kongu Engineering College, Perundurai, Tamilnadu, India
Anbarasu M: Department of Civil Engineering, Government College of Engineering, Salem, Tamilnadu, India

Abstract
Many prefabricated concrete frame joints have been proposed, and most of them showed good seismic performance. However, there are still some limitations in the proposed fabricated joints. For example, for prefabricated prestressed concrete joints, prefabricated beams and prefabricated columns are assembled as a whole by the pre-stressed steel bar and steel strand in the beams, which brings some troubles to the construction, and the reinforcement in the core area of the joints is complex, and the mechanical mechanism is not clear. Based on the current research results, a new type of fabricated joint of prestressed concrete beams and confined concrete columns is proposed. To study the seismic performance of the joint, the quasi-static test is carried out. The test results show that the nodes exhibit good ductility and energy dissipation. According to the experimental fitting method and the "fixed point pointing" law, the resilience model of this kind of nodes is established, and compared with the experimental results, the two agree well, which can provides a certain reference for elasto-plastic seismic response analysis of this type of structure. Besides, based on the analysis of the factors affecting the shear capacity of the node core area, the formula of shear capacity of the core area of the node is proposed, and the theoretical values of the formula are consistent with the experimental value.

Key Words
prefabricated joint; seismic performance; resilience model; shear capacity; node core area

Address
Li Shufeng, Zhao Di: School of Traffic and Transportation of Xu'chang University, Xu'chang, Henan, 461000, China
Li Qingning, hang Jiaolei and Yuan Dawei: School of Civil Engineering of Xi'an University of Architecture and Technology, Xi'an, Shanxi, 710055, China
Zhao Huajing: School of Science of Xi'an University of Architecture and Technology, Xi'an, Shanxi, 710055, China

Abstract
The pre-peak cyclic shear mechanism of two-order asperity degradation of rock joints in the direct shear tests with static constant normal loads (CNL) are investigated using experimental and numerical methods. The laboratory testing rock specimens contains the idealized and regular two-order triangular-shaped asperities, which represent the specific geometrical conditions of natural and irregular waviness and unevenness of rock joint surfaces, in the pre-peak cyclic shear tests. Three different shear failure patterns of two-order triangular-shaped rock joints can be found in the experiments at constant horizontal shear velocity and various static constant normal loads in the direct and pre-peak cyclic shear tests. The discrete element method is adopted to simulate the pre-peak shear failure behaviors of rock joints with two-order triangular-shaped asperities. The rock joint interfaces are simulated using a modified smooth joint model, where microscopic scale slip surfaces are applied at contacts between discrete particles in the upper and lower rock blocks. Comparing the discrete numerical results with the experimental results, the microscopic bond particle model parameters are calibrated. Effects of cyclic shear loading amplitude, static constant normal loads and initial waviness asperity angles on the pre-peak cyclic shear failure behaviors of triangular-shaped rock joints are also numerically investigated.

Key Words
Pre-peak cyclic shear; Two-order asperity degradation; Shear failure modes; DEM; Numerical simulation

Address
Xinrong Liu: School of Civil Engineering, Chongqing University, Chongqing 400045, P.R. China
Yongquan Liu: School of Civil Engineering, Chongqing University, Chongqing 400045, P.R. China; China Construction Underground Space Co., Ltd., Chengdu, 610081, P.R. China
Yuming Lu: School of Civil Engineering, Chongqing University, Chongqing 400045, P.R. China; Chongqing No.7 Construction Engineering Co., Ltd., Chongqing, 400059, P.R. China
Miaomiao Kou: School of Civil Engineering, Qingdao University of Technology, Qingdao, 266033, China
Cooperative Innovation Center of Engineering Construction and Safety in Shandong Blue Economic Zone, Qingdao, 266033, China

Abstract
The present paper is concerned at investigating the effect of hydrostatic initial stress, gravity and magnetic field in fiber-reinforced thermoelastic solid, with variable thermal conductivity. The formulation of the problem applied in the context of the three-phase-lag model, Green-Naghdi theory with energy dissipation, as well as coupled theory. The exact expressions of the considered variables by using state-space approaches are obtained. Comparisons are performed in the absence and presence of the magnetic field as well as gravity. Also, a comparison was made in the three theories in the absence and presence of variable thermal conductivity as well as hydrostatic initial stress. The study finds applications in composite engineering, geology, seismology, control system and acoustics, exploration of valuable materials beneath the earth's surface.

Key Words
Green-Naghdi theory III; three-phase-lag model; coupled theory; magnetic field; gravity; conductivity; hydrostatic initial stress

Address
Department of Mathematics, Faculty of Science, Zagazig University,P.O. Box 44519, Zagazig, Egypt

Abstract
The objective of this study was to determine the effective compressive strength of a column-slab connection with different compressive strengths between the column and slab concrete. A total of eight column specimens were fabricated, among which four specimens were restrained by slabs while the others did not have any slab, and the test results were compared with current design codes. According to ACI 318, the compressive strength of a column can be used as the effective compressive strength of the column-slab connection in design when the strength ratio of column concrete to slab concrete is less than 1.4. Even in this case, however, this study showed that the effective compressive strength decreased. The specimen with its slab-column connection zone reinforced by steel fibers showed an increased effective compressive strength compared to that of the specimen without the reinforcement, and the interior column specimens restrained with slabs reached the compressive strength of the column.

Key Words
effective compressive strength; joint; reinforced concrete; different concrete strength; failure characteristic; high strength concrete

Address
Seung-Ho Choi, Jin-Ha Hwang, Sun-Jin Han, Kang Su Kim: Department of Architectural Engineering, University of Seoul, 163 Siripdaero, Dongdaemun-gu, Seoul, 02504, Korea
Hyun Kang: Fire Research Institute, Korea Institute of Civil Engineering & Building Technology (KICT), 64, Mado-ro 182beon-gil, Mado-myeon, Hwaseong-si, Gyeonggi-do 18544, Korea
Jae-Yeon Lee: Division of Architectural Engineering, Mockwon University, 88 Doanbuk-ro, Seo-gu, Daejeon 35349, Korea

Abstract
Shear lag phenomenon has long been taken into consideration in various structural codes; however, the AISC provisions have not proposed any specific equation to calculate the shear lag ratio in some cases such as fillet-welded connections of front-to-front double channel sections. Moreover, those equations and formulas proposed by structural codes are based on the studies that were conducted on riveted and bolted connections, and can be applied to single channel sections whilst using them for fillet-welded double channels would be extremely conservative due to the symmetrical shape and the fact that bending moments will not develop in the gusset plate, resulting in less stress concentration. Numerical models are used in the present study to focus on parametric investigation of the shear lag effect on fillet-welded tension connection of double channel section to a gusset plate. The connection length, the eccentricity of axial load, the free length and the thickness of gusset plate are considered as the key factors in this study. The results are then compared to the estimates driven from the AISC-LRFD provisions and alternative equations are proposed.

Key Words
shear lag; tension members; net section fracture; double channel section

Address
Moien Barkhori: Department of Civil Engineering, University of Jiroft, Jiroft, Iran
Shervin Maleki, Meissam Nazeryan: Department of Civil Engineering, Sharif University of Technology, Tehran, Iran
Masoud Mirtaheri and S.Mahdi S.Kolbadi: Department of Civil Engineering, K.N. Toosi University of Technology, Tehran, Iran


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